1. Field of the Invention
The invention relates to a catalyst production method for preventing uneven supporting of a metal or the like supported on a support, an electrode catalyst for fuel cell produced by the method, and a catalyst production apparatus.
2. Description of Related Art
A fuel cell directly converts a chemical energy into an electrical energy by supplying a fuel and an oxidant to two electrically connected electrodes, and electrochemically effecting oxidation of the fuel. Unlike thermal power generation, the fuel cell is not restricted by the Carnot's cycle, and hence is high in energy conversion efficiency. The fuel cell is generally formed of a lamination of a plurality of single cells each having, as a basic structure, a membrane/electrode joint unit in which an electrolyte membrane is sandwiched between a pair of electrodes.
The electrode of the fuel cell generally includes an electrode catalyst. In recent years, as a production method of an electrode catalyst for fuel cell, there is a method in which a catalyst metal is supported on a support using a supercritical fluid. In Japanese Patent Application Publication No. 2000-017442 (JP 2000-017442 A), there is disclosed a method for producing a metal-supported material by obtaining the metal-supported material through a dissolution step of dissolving a metal precursor in a supercritical fluid, and preparing a precursor fluid, and a coating step of bringing the precursor fluid into contact with a base material (Claim 1 of JP 2000-017442 A).
On the other hand, in Japanese Patent Application Publication No. 2006-273613 (JP 2006-273613 A), there is disclosed a method for producing a metal-supported carbon nanostructure body, by including a treatment step of subjecting a carbon nanostructure body previously formed on a substrate, and heated to 300 to 800° C. to a contact treatment with a compound of the metal in a state dissolved in a supercritical fluid (Claims 4 and 5 of JP 2006-273613 A).
JP 2000-017442 A describes to the following effect: in the presence of a porous base material, a platinum precursor is dissolved in supercritical carbon dioxide, thereby to allow the platinum precursor to be adsorbed on the porous base material; then, the supercritical carbon dioxide is removed, and burning is performed, thereby to allow platinum to be supported on the porous base material (paragraphs [0023] to [0025] of JP 2000-017442 A). However, with such a procedure, the platinum precursor may not be adsorbed in a sufficient amount on the porous base material within a treatment time as short as less than 1 hour. FIG. 2 of JP 2006-273613 A shows a configuration diagram of an apparatus including a reaction vessel having a silicon substrate including a carbon nanostructure body formed thereon and a micro heater, a stirring vessel for accommodating a platinum catalyst dissolved in a supercritical carbon dioxide, and a valve that is able to open and close the passage between the reaction vessel and the stirring vessel as an apparatus for allowing platinum to be supported on a carbon nanostructure body. However, when such an apparatus is used, there is a possibility that the temperature of the supercritical fluid cannot be controlled with precision.